When painting door leaves with aesthetically attractive profiling, spray coating is today definitely the predominant method. As for simpler, flat door leaves, spray coating as well as curtain coating of either paint or varnish can be used.
In comparison with spray coating, curtain coating offers an economically considerably more attractive method which additionally offers larger capacity. A drawback with spray coating is the large paint losses--often exceeding 50 % or more--which inevitably arise in the spray coating process, and which also means an increased health-endangering of personnel near the apparatus. Another important drawback is that the feed speed of the object in spray coating are lower than the corresponding speed in curtain coating, which, productionwise means that the method is also more expensive.
Today, a widespread opinion is that only flat door leaves can be painted with curtain coating, since curtain coating of profiled door leaves, for instance of the panel type, results in that the so called shade side of the profiled surfaces will not obtain a satisfactory coverage of paint or varnish. The so called shade side may hereby be defined as the application surfaces facing opposite the direction of feed of the conveyor.
It is thus considered impossible to paint profiled door leaves with a satisfactory result by using curtain coating.
A known, but less successful attempt to solve the problem is to angle the conveyor in order to "get at" the shade side. However, the angling creates new shade sides and the result is thus completely unsatisfactory.
Another known attempt is to run the door leaf a first time through the curtain and then to turn the door leaf around and run it through a second time so as to also reach said shade side. Such a method is however production-wise very unsatisfactory since the capacity of the apparatus will be halved.